Cotton, wheat, corn, sorghum, soybeans, and hay or silage are typical crops that are widely grown. Harvesting these crops cannot be started in the morning until the sun has warmed the plants sufficiently to drive off dew or other moisture. Harvesting can continue until dew falls in late evening, typically long after the sun has gone down. Thus, there is a long period—often about 12 hours a day—when most crops cannot be harvested because the crop is too wet. The exact moisture conditions differ somewhat for different crops but the overall problem is the same, i.e. if the crop is too wet, harvesting has to wait because the wet crop will, rot. Sorghum, corn and other grains are a particular problem because, when harvested too wet, they cannot be fed even to livestock because of the production of certain aflatoxins.
When cotton is picked or stripped in the field, a wide variety of things accumulate in a cotton module that is transported to a gin for ginning. Picked or stripped seed cotton produces a collection of cotton lint, motes, cotton seed and gin trash, which is the industry term for dirt, leaves, stems, weeds and weed seeds. Currently, seed cotton is dumped from a picker or stripper into a module builder on the edge of a field where a large rectangular module is created by tamping the seed cotton in a large metal container. A new generation of cotton pickers produces a module which is discharged on the field, eliminating the need for a separate module builder. One of the new generation of cotton pickers produces a plastic wrapped round module.
Picking of cotton from the field does not normally start until the morning sun warms the plants sufficiently to drive off any dew or other moisture. A moisture sensor is typically used to determine the moisture content of the plant so picking can be delayed until the moisture content in the seed cotton and debris falls below some predetermined value, typically around 12%. The reason is that, at higher moisture levels, there is a risk of plant debris rotting or excessive moisture causing microbial changes in cotton fibers resulting in staining which cannot be removed before the cotton is ginned because there is often a delay of up to several months from the time cotton is picked until it is ginned. When considerable rotting or staining occurs, the cotton fibers are degraded thereby reducing the grade of the ginned cotton and thus the price obtained for it.
The cotton modules are delivered to a cotton gin where the module is stored until the gin is ready for the particular module. The module is delivered onto the conveyor of a module feeder where it is disintegrated so cotton clumps pass into the gin where the lint is separated from cotton seeds and gin trash. One of the operations in a conventional cotton gin is to heat the unprocessed cotton enough to further reduce the moisture content. This is desirable because it is much easier to separate cotton and seed from leaves, stems and the like at low moisture levels as opposed to higher moisture levels. For example, conventional gin stands operate efficiently at moisture levels in the 4-6% range while roller gin stands operate best at much lower moisture levels. In the past, almost all gins have used a natural gas, propane or LPG fired heater to heat the seed cotton and evaporate some or most of the water from the stream passing through the dryer.
It is known in the prior art to use microwaves to heat ginned cotton to counteract the effects of honeydew on cotton as shown in U.S. Pat. Nos. 4,896,400; 4,999,926; 5,008,978 and 5,048,156. It is known in the prior art to incorporate dryers in harvesters of hay, U.S. Pat. Nos. 4,912,914 and 5,105,563, and grains, U.S. Pat. Nos. 4,038,758; 4,509,273; 5,156,570; and 6,536,133. Of more general interest are the disclosures in U.S. Pat. Nos. 3,940,885; 4,640,020; 4,649,055 and 5,153,968. At least one attempt has been made to dry seed cotton in a cotton gin environment with microwaves but was unsuccessful because it popped the cotton seeds and the attempt was abandoned. Conventional domestic microwave ovens and conventional radio frequency ovens have been used to dry seed cotton in a laboratory in a research project to estimate cotton yields early in the season at a time before the bolls open.